Switching systems (also referred to as “switching networks”) route data through and among data communications networks. Switching systems typically comprise a plurality of switches and clusters of switches (“nodes”) that provide data communications paths among elements of data communications networks.
The “topology” of a switching network refers to the particular arrangement and interconnections (both physical and logical) of the nodes of a switching network. Knowledge of the topology of a switching network is used to compute communications paths through the network.
For switching systems that comprise a small number of individual switches, the topology is fairly straightforward and can be described by identifying the individual nodes in the system and the communications links between them. For larger and more complex networks, however, the amount of data needed to identify all links between all nodes of the network can be quite extensive.
A number of approaches have been proposed to reduce the amount of information needed to describe the topology of complex switching networks. One approach involves grouping physical nodes into groups (“peer groups”) that are viewed as individual logical nodes (“logical group nodes”) having characteristics that comprise an aggregation of the characteristics of the individual nodes within the group. Such logical group nodes may be further grouped with other physical and/or logical nodes to form successively higher level peer groups, creating a hierarchy of peer groups and logical group nodes.
One example of a network that allows physical nodes to be grouped into levels of logical groups of nodes is a “PNNI” network. PNNI, which stands for either “Private Network Node Interface” or “Private Network Network Interface,” is a routing and signaling protocol developed by the ATM Forum. The PNNI routing protocol is used to distribute topology information between switches and clusters of switches within a private ATM switching network. The PNNI signaling protocol is used to set up data connections within the PNNI network, via signaling call setup messages through the network.
A PNNI network is a network that utilizes the PNNI routing and signaling protocol. Within the PNNI routing protocol a Logical Group Node (LGN) is an abstract representation of a lower level Peer Group (PG) as a single point for the purposes of operating at one level of the PNNI routing hierarchy. Logical Group Nodes are created in a switching system via configuration and become operational dynamically as a result of the PNNI routing protocol behavior. Within the PNNI routing hierarchy a lowest level node is an abstraction representing a single instance of the PNNI routing protocol. Lowest level nodes are created in a switching system via configuration and are always operational. An LGN or a lowest level node is also known as a logical node or a node for the purpose of the present application.
The PNNI routing protocol is used typically in ATM products to distribute information about changing network topology and network resources among a group of associated switches. Topology information is organized and distributed in a hierarchical fashion, or a flat single peer group, depending on the network topology. Hierarchy allows networks to scale their topologies to a very large number of nodes. The PNNI implementation provides the required support to exist and participate in the multilevel hierarchical network.
In a hierarchical network, nodes in the PNNI routing domain are grouped into peer groups. Nodes in the same peer group elect a peer group leader. The peer group leader is responsible for activating a logical group node (LGN) at the second level of hierarchy as well as existing as the logical node in the lowest level. The newly activated LGN exchanges PNNI routing information with other neighbor LGNs at the second level of hierarchy. The neighbor LGNs are other LGNs that other lower level PGLs instantiated from adjacent peer groups. In addition to exchanging information the LGN propagates information from higher levels down into the lower level peer group via the PGL that instantiated it. This is so that all nodes in the lower level peer group have the same information about the other LGNs in the higher level peer group where the activated LGN exists. From the hierarchical topology information gathered by a node, routing tables are created and used by the switches to route calls using the PNNI signaling protocol. PNNI networks and hierarchical groupings are described in co-pending U.S. application entitled “Method for Advertising Reachable Address Information in a Network” the contents of which are incorporated herein by reference.
In the present invention, networks use a logical hierarchical grouping of nodes, e.g. PNNI enabled ATM networks, to reduce the amount of routing information that is distributed and stored throughout the network. More specifically, the invention is directed to the problem of ensuring the stability of the control plane, particularly SVCC routing control channel (RCC) connections. These connections are set up between PNNI peer group leader (PGL) nodes (or logical nodes in higher level peer groups) in different peer groups (PG) to exchange information (e.g. routing, topology, and reachability information) between the groups. With the introduction of new and future features such as Restricted Transit and Policy-based Routing, limitations and additional criteria are placed on the routing and establishment of connections. Ensuring that SVCC-RCC connections are not adversely affected by provisioning changes made to the network to support these features is and will be very important to guaranteeing high levels of network reliability, availability, and serviceability (RAS), since SVCC-RCC connections are integral to the PNNI control plane.
Ensuring that SVCC-RCC connections are not adversely affected by provisioning changes has not as yet been addressed in the industry mostly because SVCC-RCC connections typically require little attention after they have been created. They are created when a PNNI PGL node is elected and remain established while the network is operating. However, if an SVCC-RCC connection were to be dropped, e.g. because of an equipment failure or maintenance action, features like Restricted Transit and Policy-based Routing could prevent the connection from being re-created, which would negatively impact network services since the PNNI control plane would not come back up. As route and connection establishment limiting features such as Restricted Transit and Policy-based Routing become more prevalent in networks, and as the number of SVCC-RCC connections in large networks continues to increase into the hundreds, ensuring SVCC-RCC connections remain unaffected by provisioning changes will gain more attention in the industry.
There is, therefore, a need to provide systems and methods of monitoring the control plane in networks such as PNNI networks.